The present invention relates to a method and an apparatus for forming a pattern where a pattern is formed by discharging a viscous pattern forming material to a pattern forming object through a pattern forming mask having a predetermined opening pattern with respect to the pattern forming object.
As a method for forming a pattern on a pattern forming object, a pattern forming method which uses a screen mask is used in general.
The pattern forming method using a screen mask is a type of stencil pattern forming method where a paste (pattern forming material) such as ink is made to pass through a pattern forming mask having an opening pattern by squeezing (extruding the paste (pattern forming material)) by a squeegee thus transferring a desired pattern on a pattern forming object. This pattern forming method using a screen mask is used in various applications such as the formation of printed circuit wiring of an IC substrate or the formation of a pattern (formation of electrode and filling of phosphor) on an FDP (Flat Display Panel).
A mesh mask, a metal mask or the like is used as a pattern forming mask.
A mesh mask is a mask where an opening pattern is formed on a knitted material made of mesh-like stainless steel, polyester or the like using a photosensitive emulsion. For enhancing pattern forming accuracy, a mask where opening pattern is formed on a metal mesh which exhibits small deformation is popularly used.
A metal mask is a mask where an opening pattern is formed on a metal plate by laser forming, etching or the like or a mask where an opening pattern is formed on a metal plate by plating.
A pattern forming method using a screen mask is used in various pattern formations such as the pattern formation of electrode wiring, solder resist, flux or solder paste on various electronic devices or printed circuit boards, the pattern formation of a frame-like sealing material on substrate for a liquid crystal display, the pattern formation of a dielectric layer on a substrate for a plasma display, partition walls between pixels, electrode wiring and fluorescent material. A size of the mesh mask, that is, an area of a mesh, a size of a mask printing frame for pattern forming, a width of a tension mesh and the like are designed in conformity with the application.
A method for forming a pattern on a pattern forming object through a pattern forming mask substantially includes a step of filling a viscous pattern forming material (paste) into an opening pattern portion formed on a pattern forming mask, and a step of transferring the viscous pattern forming material (paste) filled into the opening pattern portion formed on the pattern forming mask to the pattern forming object through the pattern forming mask.
A pattern forming method using a screen mask uses, in general, a scraper for applying a viscous pattern forming material (paste) to a pattern forming mask by coating or a squeegee for filling a viscous pattern forming material (paste) into the inside of an opening pattern portion formed on a pattern forming mask.
On the other hand, as a method of filling a viscous pattern forming material (cream solder) in a pattern forming mask, JP-A-2000-62138 discloses a method which uses a pressurizing means in place of a scraper or a squeegee used in general in a pattern forming method using the screen mask. Further, JP-A-11-268236 discloses a method which uses a forcibly pressurizing discharge mechanism part as a method of filling a viscous pattern forming material (paste) into a pattern forming mask. These conventional examples are referred to as pressurizing discharge means hereinafter.
According to these conventional examples, a filling pressure can be controlled with high accuracy, a viscous pattern forming material can be filled into the opening portion formed in pattern forming mask from a discharge port at an appropriate filling pressure, and filling of the paste is hardly influenced by physical properties such as viscosity or viscoelasticity of the paste. Further, the paste is accumulated in the hermetic structure of a discharge mechanical part and hence, a change in physical property of the paste at the time of forming a pattern (the increase of viscosity caused by evaporation of a solvent or the like when the paste is left on a pattern forming mask or inclusion of dry solid material) can be prevented, and also entrapment of air or dust in the paste can be prevented.
Further, JP-2011-152487 discloses, as a method for forming a pattern of a solar cell, a method where a material is linearly supplied from a nozzle without using a pattern forming mask.
According to this conventional example, for example, in forming a finger electrode which intersects with a bus electrode, a pattern of the finger electrode can be formed with a large film thickness (high aspect ratio), and it is possible to prevent a surface of the finger electrode at an intersecting position from becoming uneven.
A pattern forming object used in a solar cell is cut out from a silicon ingot by a wire saw. However, there is irregularity in thickness in the pattern forming object, and also the flatness of the pattern forming object is not uniform. Further, there is a tendency that a thickness of the pattern forming object used in a solar cell is made small for enhancing light emitting efficiency and hence, the pattern forming object warps or waves. Accordingly, it is difficult to bring a pattern forming mask into uniform contact with a pattern forming object over the whole surface.
In the conventional screen printing method, it is necessary to bring the pattern forming mask into contact with the whole surface of the pattern forming object by applying a printing pressure to the squeegee. Accordingly, in stroking the squeegee on the pattern forming mask, there arises a drawback that the pattern forming mask is damaged by an edge of the pattern forming object used in a solar cell. When a thickness of the pattern forming object used in the solar cell is uniform, by arranging a substrate having the same thickness as the pattern forming object around the pattern forming object thus eliminating a stepped portion, it is possible to prevent breaking of the pattern forming mask. When the thickness of the pattern forming object is not uniform, there arises a drawback in the pattern formation due to the difference in thickness between the pattern forming object and the substrate.
As means for obviating such a drawback, a method for forming a pattern in a state where a pattern forming mask and a pattern forming object are not in contact with each other is proposed and, the method is disclosed in JP-A-2003-25706.
According to this conventional example, ink is filled into an opening portion formed in the pattern forming mask by a scraper, and high pressure gas is sprayed from a nozzle in the direction toward the pattern forming object from the pattern forming mask thus forming a pattern without bringing the mask into contact with a substrate.